1. Field of the Invention
The present invention relates to the manufacture of golf club heads. Particularly to the manufacture of a golf club head with an improved center of gravity and moment of inertia.
2. Description of the Related Art
As driver golf club heads have increased in volume (>300 cubic centimeters) their moments of inertia have also increased, providing greater forgiveness for off-center hits. The conventional method for enlargement of golf club heads was to maximize the spatial distribution of mass in all three orthogonal orientations. Although this approach was effective in increasing the moments of inertia of the golf club heads, it also resulted in the center of gravity of the golf club head being positioned substantially rearward from the front face of the golf club head.
As the center of gravity is positioned further rearward from the front face, deleterious effects result for shots struck off-center from the sweet spot of the golf club head. Increased gear effect is the main cause of the deleterious effects. For heel-ward or toe-ward off-center hits, the increased gear effect can cause increased side-spin, which increases dispersion, reduces distance and reduces robustness of ball flight. For off-center hits above the sweet spot, the increased gear effect causes reduced backspin, which can cause an undesirable trajectory having insufficient carry length or time of flight, which in turn can result in reduced distance and reduced robustness.
In addition, the same conventional golf club head designs are limited with regard to the maximum face area, both physical and practical limitations. The physical limitation is due to the golf club head having insufficient mass to both increase the length and width of the golf club head and also to increase the face size without exceeding the upper range of the preferred total golf club head mass. Such mass distributions are dependent on minimum wall thickness values required to achieve acceptable in-service durability.
The practical limitation is that as the face size is increased, hit locations in certain regions around the face perimeter will yield an unsatisfactory ball flight due to the aforementioned deleterious effects, which are accentuated for larger faces. The deleterious effects increase in a non-linear manner as the distance from the face center increases. Thus the incremental face area gained by increasing face size will be subject to more extreme deleterious effects. This limits the practical length of the club, because probable hit distribution across the surface of the face broadens as the club length increases. As a result a longer club will yield a larger percentage of hits in the perimeter regions of the face where the deleterious effects occur. This offsets the otherwise beneficial effect of increased head speed. As club length increases, head speed increases up to a length of approximately 52 inches, at which point aerodynamic and biomechanical effects offset the length effect.
Further, conventional head designs having a center of gravity positioned substantially rearward from the face are subject to significant dynamic loft effects, which can be undesirable. Dynamic loft increases with head speed, so that golfers with higher head speeds experience more dynamic loft than those with slower swing speeds. This is opposite of what is desired as higher head speeds generally require less loft, otherwise excess backspin will be generated, which negatively affects trajectory and performance.
Currently, golf club heads made of metal, composite, or other material are produced with a specific weight which is fixed once the golf club head is finished. The fixed weight of the golf club head determines the center of gravity and moment of inertia. After the golf club head is finished, there exists a small amount of weight which needs to be adjusted. This small amount of weight is called the swing weight. Presently, if the swing weight needs to be adjusted, to alter the center of gravity and/or moment of inertia, the fixed weight must be changed, which requires the manufacture of a new golf club head.
One invention that addresses a golf club head with an improved moment of inertia and center of gravity is U.S. Pat. No. 7,559,851 issued to Cackett et al. for Golf Club Head with High Moment of Inertia. This patent discloses a golf club head with a moment of inertia, Izz, about the center of gravity of the golf club head that exceeds 5000 grams-centimeters squared
Another example is U.S. Pat. No. 3,897,066 to Belmont which discloses a wooden golf club head having removably inserted weight adjustment members. The members are parallel to a central vertical axis running from the face section to the rear section of the club head and perpendicular to the crown to toe axis. The weight adjustment members may be held in place by the use of capsules filled with polyurethane resin, which can also be used to form the faceplate. The capsules have openings on a rear surface of the club head with covers to provide access to adjust the weight means.
Yet another example is U.S. Pat. No. 2,750,194 to Clark which discloses a wooden golf club head with weight adjustment means. The golf club head includes a tray member with sides and bottom for holding the weight adjustment preferably cast or formed integrally with the heel plate. The heel plate with attached weight member is inserted into the head of the golf club via an opening.
It is the object of this invention to adjust the swing weight of the golf club head externally, without having to manufacture a new golf club head. The golfer will be able to adjust the center of gravity and moment of inertia to best suit his or her playing needs. The golf club head has external weights positioned at specific locations on the golf club head body to improve the center of gravity and moment of inertia characteristics. The weights to be inserted into the cavities of the golf club head are all of the same size and shape, however vary in density. This allows for the weights to be interchangeable depending on the golfer's individual needs. The aft-body of the golf club head is preferably composed of a composite material with recessed cavities to engage the weights. In the center bottom of the recessed cavities, a timesert is comolded when the composite aft-body is manufactured. Once the composite material is cured, the timesert is permanently bonded to the golf club head body. A bolt is used to fasten the weight to the body. The walls of the recessed cavities have a 20 degree taper to engage the weight and produce a tight fit. The tapered walls are in contact with the weights and receive the force of impact when the golf club is used. A main feature of the present invention is the ability to externally adjust the weight of a golf club head having a composite aft-body. The ability to remove and reposition the weights to other locations on the body, after manufacture, is a novel feature.